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If your going to use the dryer vent to the greenhouse, make sure you have another lint filter on the line besides the one on the dryer. Our vent line broke and I thought I'd keep the garage warm for the cats last winter by not fixing the vent to the outside. Never do that again. I had lint all over the place even though we had a good lint catcher on the dryer.

I suggest you google INDOOR LINT TRAPS and see what you can find. This will save a lot of headaches with the lint problem.

yea i remember back in 2000 i rented a apt that did not have a dryer vent leading to the outside. we had to use a little box that held water to catch the lint. good idea on that. cause i remember haveing to clean it alot and keep up with it or lint would be everywhere.

@white95v6 wrote:it is two 12ft x 4ft beds with a walkway in the middle about 2.5-3ft wide. i would cover the whole area. and have the barrels in the walkway area.

One downfall with that arrangement, is that if the sun is shining, you have to vent your hoop house, which drops your potential ambient temp, so your heat absorption by your barrels is strictly from the sun's radiation. Water in a garden hose heats quickly and hot because the surface area of the hose is large compared to the volume of water inside. In a jug or barrel, you don't have adequate surface area to create a significant temp change for the large volume inside. You would be way ahead if you could attach radiator type fins to your barrels to drastically increase your apparent surface area.

This is something I tried a couple years ago...in the summer time. My problem here in the summer is cool nights. Warm crops like toms and corn just can't accumulate enough GDDs in a growing season.

I would cover the whole affair with plastic at night. Temp swings from 50ish at night to 80ish during the day. The barrels just didn't accumulate enough heat during the day to make a difference at night. I had three identical plants in the ground, and there wasn't any significant difference in maturation time or harvest.